This invention relates to AC electric current control systems, such as motor controllers and illumination switches.
The connection of AC power controllers with the wiring of buildings is usually obtainable only with one side of the AC power line. For example, the wire for the switch circuit from a ceiling or porch light is often connected with the hot side of the AC circuit being the only line switched. Therefore, full line power is not available at most wall switch locations. As a result of this wiring practice, it is necessary that any electrical device intended to find popular acceptance as a replacement for a wall-mounted switch must rely upon merely the power present in the one side of the circuit. Such a device must be connected in series with the load and the AC power source.
Also, wall-mounted switch controllers which include dimmers, time-delay devices, emergency flashing devices, variable intensity controllers, and motor controllers are designed as dedicated devices that serve one function and usually are designed where the full line power is available. If not available, then additional wiring is needed.
Weber in U.S. Pat. No. 4,300,090 and Dubot et al in U.S. Pat. No. 4,754,213 disclose a technique to provide DC power supply by taking the pre-conduction potential which is developed across a thyristor. This potential is derived by fixing the turn-on voltage by zener diodes. The AC power is rectified and filtered to provide low voltage direct current. This requires a thyristor to provide the voltage drop and another thyristor or relay to control the load device current.
Weber noted this deficiency in U.S. Pat. No. 4,878,010 where he uses a slightly different technique in which the thyristor is used for both deriving low voltage DC power and also as the control device. In this patent, Weber derives the power from the zener drop during ON and OFF times to provide the low-voltage DC power. He controls the thyristor by allowing the zener current to the thyristor or diverts the current flow away from the gate of the thyristor to other side of the circuit using a shunting scheme. The turn-on potential of the gate along with the zener voltage sets the low voltage DC power when the thyristor is ON and shunting transistor with the zener voltage sets the low voltage DC power when the thyristor is OFF. Depending on the thyristor gate voltage, the low voltage DC will be at different levels for the control circuits. Also, Weber discloses in U.S. Pat. No. 4,878,010 a technique to provide AC power control using one side of the AC lines. His technique is limited to charging a capacitor every other half cycle, on only the positive-going AC cycles. Therefore, to maintain the necessary power for the complete cycle, Weber needs to use a much larger capacitor for the storage of the DC power then if one uses every half cycles of AC power. Furthermore, he needs to use thyristors that have sensitive gate control, which are more expensive than typical thyristors. In addition, Weber shows several dedicated configurations for each type of functions, which requires extensive hardware redesign for each function.
Other references shown have circuits which use a microcontroller, but derive their power from charging a large capacitor, batteries, transformers, or are designed to have both AC lines available. Here is the summary of the different schemes which have been proposed to provide power to the control circuitry:
In U.S. Pat. No. 4,878,010, the device turns ON at a fixed voltage level and provides power during the time the load is powered. However, the device must use a very large capacitor because the device derives power every cycle, and uses a dedicated circuitry. Also, the fixed voltage level limits the usefulness of the device to ON and OFF operations.
In U.S. Pat. No. 4,754,213, the device uses a thyristor and a large power relay in series. It fixes the ON voltage to a certain level, and uses a dedicated circuitry.
In U.S. Pat. No. 4,924,109, the device use the same technique as U.S. Pat. No. 4,878,010 and allows for a 30-50% DIM operation.
In U.S. Pat. No. 5,481,452, the device has a programmable controller, but derives power from a transformer which is connected to both leads of the AC source, or from a battery when one lead is only available.
In U.S. Pat. No. 5,573,983, the device has a programmable controller, but has a dedicated power supply derived from both AC lines.
In U.S. Pat. No. 4,733,138, the device requires two AC power lines for power.
In U.S. Pat. No. 4,733,138, the device requires a two AC power lines which are coupled by a transformer to derive the DC power supply.
In U.S. Pat. No. 4,649,323, the device has a microcontroller and a zero-crossing detector, but uses dedicated DC power supply which is derived from both AC power lines. It requires a choke to operate, and only the switches are wall-mounted.
In U.S. Pat. No. 5,319,283, the device requires a large capacitor to keep power when the device provides power to the AC load. It also requires two thyristors for controlling the switching operation.
In U.S. Pat. No. 5,811,963, the device charges the large capacitor during the time when the AC load is not being provided power. During the time when the AC load requires power, the device uses the DC power from the stored power in the capacitor. If the power is required continuously, this scheme is not effective.
The disadvantages of the prior art are as follows:
a. more and higher cost components;
b. limited flexibility for features and functions;
c. not a single wire line device, and therefore can not be use in older dwellings.
Accordingly, there has heretofore existed a need for an inexpensive and effective system for providing an AC power controller who derives its power from series connection between the AC power source and AC load.
The present invention provides a highly versatile microcomputer-controlled switch operating in series with an AC circuit that is installed between an AC load such as a light fixture, and the source for the AC power. This versatile switch controller derives DC power form the AC circuit, which is in series with the AC load and AC power, by stealing a small portion of the AC power every half cycle. This AC power is rectified for each half cycle and is used to maintain a small capacitor charge during the times when controller has turned ON power to the load.
In previous inventions, the capacitor needs to be large enough to maintain DC power for a full cycle or more such as noted in Weber U.S. Pat. No. 4,878,010 or required two thyristors such as U.S. Pat. No. 4,745,213. In both these cases, ""010 and ""213, the AC voltage used was fixed based on the external connected zeners. The problem with these arrangements is that fixing the voltage where the thyristor turns ON limits the device to ON and OFF operations and does not lend itself to dimming functionality. In this invention, by contrast, the amount of AC voltage can vary or be fixed depending on the microcontroller or circuitry. If one needs to dim the lights or slow down the motor, than the AC voltage would be switch ON at any portion of the AC cycle.
Since this design utilizes an isolation thyristor driver such as a relay or optoisolator driver, the microcontroller can easily be programmed to turn the power to the AC load ON and OFF, similar to if one were to use a controller with a dedicated power supply. The controller only needs to provide gate current pulse at the beginning of every halfcycle to enable the thyristor. Once the thyristor is provided with a gate current, it turns ON. The thyristor stays ON even without any further current in the gate until the AC voltage goes back to zero.
The primary object of the invention is the technique to provide power to the controller by stealing a portion of the AC power at the beginning of the half cycle and to provide the gate current pulse to enable the thyristor. During any portion of the half cycle, the controller can initiate an ON cycle by providing a gate current pulse. Once initiated, the thyristor takes over until the end of the half cycle zero crossing. The controller can maintain an OFF condition by not providing the gate current pulse.
A further object of this invention is to provide a light level controller, which includes an automated fade function, which gradually fades the light intensity level from a full ON to an OFF condition.
Another object of this invention is to provide a light controller which the light is turned ON and OFF at long random times from minutes to hours. This simulates that the house is lived in and deters burglars.
Another object of this invention is to provide a light controller, which has an attention-getting mode that flashes the light from full brightness to dim at a fast, periodic rate. This light controller if installed in the front porch light electrical circuit would help delivery personnel locate the house.
Another object of this invention is a light controller, which dims the light level for a period of minutes and then turns the light OFF. This light controller would be used in a child""s bedroom to allow for a quiet time before the light goes off completely.
Another object of this invention is a three-position switch where one position selects the power controller, which allows for different modes. The other two positions would be full ON and full OFF.